The broad objectives of the proposed research are to gain insight into the influence of cholinoceptive neurons on central thermoregulatory activity in the rhesus monkey, to determine whether cholinergic transmission is involved in normal thermoregulation, and to further elucidate the neuroanatomical substrate of the central thermoregulatory apparatus. With the aid of the intracerebral microinjection technic, the thermoregulatory effects of cholinergic stimulation of various diencephalic loci, including the hypothalamus and the septal region, and of an epithalamic structure, the habenular complex, will be determined, and the receptor specificity of the various responses will be examined. To determine whether cholinergic synapses are actively involved in normal thermoregulation, an attempt will be made to mimic the observed effects of cholinergic agonists by microinjection of anticholinersterases, to block ongoing thermoregulation with cholinergic antagonists or hemicholinium-3, and to detect (using subcortical push- pull perfusion) an augmented release of endogenous acetylcholine during thermoregulation evoked by thermal stress. In addition, the tremor evoked by cholinergic stimulation of the above mentioned structures and that evoked by stimulation of the caudate nucleus will be examined and compared by power density spectral analysis in order to determine whether either or both of these tremor activities are related to physiological shivering.